John Gruber has found out that cross-compilers are no longer allowed in iPhone OS 4.0. "My reading of this new language is that cross-compilers, such as the Flash-to-iPhone compiler in Adobe's upcoming Flash Professional CS5 release, are prohibited. This also bans apps compiled using MonoTouch - a tool that compiles C# and .NET apps to the iPhone. It's unclear what this means for tools like Titanium and PhoneGap, which let developers write JavaScript code that runs in WebKit inside a native iPhone app wrapper. They might be OK."